Fix Carrier settings crash issue

When world_phone enabled, "carrier settings" option
present in Mobile Network Settings menu and if we
select on it there is a crash in PhoneApp.

To fix it, modify "enabled_networks_key" handling properly
to do not display "carrier settings" menu option when
config config_carrier_settings_enable is set to false

Change-Id: Ie5fc1f60872cbed7ad82098df01720b77d88b453
3 files changed